1. Field of the Invention
The present invention relates to a photoelectric converter for wireless communication, more particularly relates to a photoelectric converter for wireless communication that converts a signal transmitted via an optical fiber to a microwave signal or receives a microwave signal conversely transmitted from terminal equipment and converts it to a signal for transmitting to an optical fiber in a field of wireless communication utilizing microwave photonics.
2. Description of the Related Art
For the embodiment of a concept that a microwave or a submillimeter wave is transmitted via an optical fiber, a remote antenna used in a community antenna television (CATV) system has been widely known and is currently in practical use. Actually, a system that a broadcast signal received via a (passive) antenna installed on a mountain apart by a few km is transmitted to a village at the foot via an optical fiber and television is watched there is implemented and for example, Kazuhisa Haeiwa et al. propose a TV wave receiving system shown in FIG. 8 on pp. 249 to 255 of xe2x80x9cTV Wave Receiving System Using Optical Modulatorxe2x80x9d in a collection C-I, J79-C-I, 7 published in 1996 by the Institute of Electronics, Information and Communication Engineers.
In the meantime, recently, demand for mass wireless communication (for example, approximately 155 Mbps), compared with the quantity of wireless communication so far is increasing and particularly, application that a microwave and a millimeter wave with a high frequency band of approximately 10 and a few GHz to a few tens GHz including so-called microwave and millimeter wave which can still handle the problem of the exhaustion of a frequency due to a mobile telephone as a base band are transmitted via an optical fiber and application to LAN for example are also desired. However, a high-frequency electric signal such as a microwave and a millimeter wave is greatly attenuated when it is transmitted in air. Therefore, for application to LAN, a base station is required to be provided in each room in a building and picocell communication is required to be executed.
For such wireless communication, there is two-way communication including a downlink where a lightwave in which a signal is superimposed is transmitted from a central station to a base station, is converted to an electric signal at the base station and the converted electric signal is transmitted from an antenna of the base station to a terminal station and an uplink where an electric signal (a radio wave) transmitted from a terminal station is converted to an optical signal at a base station and is transmitted to a central station.
As the number of base stations becomes enormous for picocell communication for implementing a high frequency in future, a base station as simple as possible is desired.
For a simple base station, Kenzo Nishikawa et al. report the configuration of a base station employing a nonlinear photodetection scheme of a photodiode on pp. 52 to 58 of xe2x80x9cMillimeter-Wave Photonic Passive Base Station Employing the Nonlinear Photodetection Schemexe2x80x9d published in Second Microwave Photonics Workshop (MPW97) of Shingakugiho, however, only a downlink is currently implemented and if this scheme can be applied to an uplink in future, actual use will be enabled. Also, as described in M. Izutsu et al., xe2x80x9cTurning properties of microwave-light wave mixing by MESFETsxe2x80x9d, Tech. Digest of URSI96, Lille, September 1996, for a downlink, the conversion of optical signal to a radio wave using a photodiode (PD) and a three-terminal element such as MESFET and HEMT is possible to some extent. The problem has been in how simple a system an uplink can be configured.
Also, in D. Wake et al., Passive picocell: a new concept in wireless network infrastructurexe2x80x9d, Electronics Letters, Vol.33, No.5, pp. 404 to 406, 1997, a two-way communication system using an electron absorption modulator (EAM) shown in FIG. 9 is proposed as a system implementable in a part of a microwave band. However, signal strength is still weak and for a complete passive type, it is difficult to apply the system except a picocell of approximately 6 m at 3 Mbps. For practical use, technical breakthrough for a high frequency for the enhancement of sensitivity and speedup is required. Also, in an example of the electron absorption modulator, a light source is installed on the side of a central station and light transmitted from the central station is used, however, in this case, application to LAN in a building having plural base stations requires complicated control over light and others, which is a problem in practical use. In addition, an EAM is very expensive.
Further, in G. H. Smith et al., xe2x80x9cFull-duplex fiber-wireless system using electrical and optical SSB modulation for efficient broadband millimeter-wave transportxe2x80x9d, Proc.MWP97, Duisburg, pp. 223 to 226, 1997, a report is described that a down stream of 155 Mbps and an up stream of approximately 50 Mbps are possible using a millimeter wave band of 38 GHz, though it is currently at a testing stage. However, the proposed system is a very large-scale system, and the installation of a base station in each room in a building and operation based upon a picocell cannot be implemented.
As described above, heretofore, for an example that two-way communication is implemented by one element, there is only an example that the electron absorption modulator shown in FIG. 9 is used for a base station. In the meantime, for a downlink, there are various reports of an element which can include a simple base station, however, the configuration of a simple base station for enabling an uplink is currently hardly implemented. Therefore, the development of a base station using as simple an element as possible to which up to a few tens GHz band which is a so-called (quasi-)millimeter wave band can be applied has been desired.
The present invention provides a photoelectric converter for wireless communication that functions as the center of a base station for providing a base station which is simple, can be manufactured at low cost and meets sufficient performance in a high frequency band. Also, the invention provides a photoelectric converter for wireless communication which can have a base station for two-way communication including an uplink and a downlink by one element.
The photoelectric converter for wireless communication according to the invention includes a laser having a first resonance mirror and a second resonance mirror, a third mirror into which a laser beam emitted from the laser enters, a channel provided between the third mirror and the laser, through which the laser beam emitted from the laser is transmitted, and plural electrodes that supply electrical energy to the channel.
Also, according to another aspect of the present invention, the photoelectric converter includes a laser having a first resonation mirror and a second resonation mirror, a mirror electrode into which a laser beam emitted from the laser enters, a channel provided between the mirror electrode and the laser, through which the laser beam emitted from the laser is transmitted, and plural electrodes, including the mirror electrode, that supply electrical energy to the channel.
In the case where the photoelectric converter for wireless communication according to the invention is used for an element for an uplink, a depletion layer in the channel varies in thickness according to the electrical energy supplied by at least one of the plural electrodes and the incident laser beam is modulated. In the case where the third mirror is a mirror electrode, the depletion layer in the channel varies in thickness according to the electrical energy supplied by the mirror electrode and the incident laser beam is modulated.
In the meantime, in the case where the photoelectric converter for wireless communication is used for an element for a downlink, a photocarrier is generated according to a signal entered into the channel together with the laser beam, and the electrical energy supplied by at least one of the electrodes is modulated.
Also, according to another aspect of the present invention, the photoelectric converter for wireless communication includes a vertical cavity surface emitting laser having a first mirror and a second mirrors, a mirror electrode constituting a cavity together with a vertical cavity of the vertical cavity surface emitting laser and provided in the cavity, a channel provided between the mirror electrode and the vertical cavity surface emitting laser, through which a laser beam emitted from the laser is transmitted, and plural electrodes, including the mirror electrode that supply electrical energy to the channel.